This house was built in 1908. The "garage" may have been built later in the 1920s when the house was upgraded to CENTRAL coal fired heating. That required a greater use of coal than the older pot belly stove systems. People began getting large deliveries and needed a place for the coal ~ so they dug basements, put in the heating systems and took delivery in a covered, enclosed shelter in the back.
The coal chute has to be somewhere ~ may have been covered over but with certainty it exists ~ they are difficult to REMOVE so folks just left them in place.
The problem with an entry door on the shared wall between garage and house is that, from the pics we have here, there is only one place it could be. That is near the front of the garage right next to the front wall. If there were to be a stairway from the basement up to the garage level the headroom needed for the stairwell would be very visible through the glass of the door on the stoop. The top of the stairwell, at the entry door to the garage, would begin about mid-way up the door on the stoop and cross it at an angle downward corresponding to the angle that the stairway descended. The stoop door would be unusable.